The present invention relates to an illumination apparatus and/or the production of a planar light output.
The illuminants (lamps) dominant in today's general illumination technology are incandescent lamps and fluorescent tubes, first realized about 120 and 60 years ago, respectively. Their technologies of manufacture and their functionalities largely are fully developed. In the past decade, substantial improvements were no longer achieved.
During the last decade, LEDs, i.e. light-emitting diodes (LED=light-emitting diode), made of semiconductors have reached a state of development by far exceeding their original functionalities and fields of employment (indicator, status and signal lamps, display technology). Today, LEDs have already started penetrating display technology for outside as well as special fields of illumination and background lighting.
Gradual penetration of the sector of general illumination by LEDs still necessitates very significant advances in the reduction of LED manufacturing costs and consumer retail prices. If the latter is achieved to a sufficient extent, the vision of “solid state lighting” may become the illumination technology of the 21st century.
The driving forces in this development are the advantages and the benefits LEDs offer as compared with conventional light sources. The prominent advantages of semiconductor-based LEDs are:                Compact construction (dimensions of few mm)        Robustness (no fragile glass components)        Low operating temperatures        Low operating voltages (few volts), mobile device operation (batteries)        Fast modulation capacity, partially e.g. above 100 MHz        Long life of more than 10,000 h, for example        Highest potential power efficiency of all electric illuminants        High point luminance        Environmental compatibility (e.g. no mercury disposal).        
Lamps on the basis of organic light-emitting diodes (OLEDs) are still in the development phase, as opposed to LEDs, but now already show significant potential as the illumination sources of the future.
Through the fast increase in efficiency of these light-emitting diodes, which today already outperform the inorganic light-emitting diodes in the case of green diodes, OLEDs open up a future market for planar illumination. As a planar luminaire with moderate luminance as compared with the LED, the OLED is ideally suited for the production of planar diffuse light sources. In the future, the OLED may here also allow for the realization of flexible luminaires due to its thin-layer technology, which permits completely new applications in the illumination of rooms. The advantages of the OLEDs are:                Planar, diffuse light source        Very thin construction (thickness of below one to few mm)        Low operating voltages (few volts), mobile device operation (batteries)        High power efficiency        Environmental compatibility (no mercury disposal)        Realization possible on flexible undersurfaces        
The possibility of a completely new kind of electric light production being obtainable by semiconductor light emission devices arose due to the III-V semiconductor (SC) technology starting in the early 1960s. In an III-V SC pn-junction, electrons and holes are injected in a spatially narrow limited area where they recombine under the emission of light. The radiation is largely monochromatic, and its wavelength is determined by the band gap of the SC material. Color LEDs are used mainly in electronics or in status indications. White LEDs, which are based on the principle of partial luminescence conversion of the blue primary light of an LED chip to a yellow-emitting illuminant, and/or color-change LEDs (constructed of three color LEDs), are mainly employed for the field of effect illumination and general illumination. The point brightness of the LEDs has increased sharply in the last few years and today reaches several millions of cd/m2, which makes employment in headlight units possible.
An important market of the future here is the background illumination of LCDs. If a planar light source with LEDs is to be realized, there are two methods for realization. On the one hand, directly radiating LEDs with an upstream diffuser are applied for the planar illumination. The disadvantage here is the diffuser, which homogenizes the more effectively, the greater the distance is to the light-emitting diode. This increases the thickness of the realized illumination areas and may also lead to angle dependencies in the color spectrum. Another possibility is the lateral radiation of LEDs with wedge optics or scattering foil optics, by which the laterally radiated light is diverted in the viewing direction. Here, the dimensioning of the scattering foil/wedge optics is complicated in order to avoid inhomogeneities in the area. Furthermore, the lateral launching achieves less efficiency, because light is absorbed in the diversion.
Electroluminescence from organic materials was first discovered in anthracene single crystals in 1963. Based thereon, the first light-emitting diodes of thin organic layers could be presented by Tang and VanSylke in 1987. In the simplest case, an OLED consists of an organic layer disposed between two electrodes (anode and cathode). As an anode, often ITO (indium tin oxide) coated glass substrates are used, which are sufficiently conductive and transparent in the visible spectral range, so that the produced light may exit through this electrode. In contrast to LEDs, OLEDs have a comparably lower brightness of 100-5000 cd/m2, which makes them suitable for direct-view illumination, but not for point-light applications. Since OLEDs are based on amorphous layers, they do not require any crystalline undersurface and may be deposited on almost any undersurfaces. White OLEDs are obtained through color combinations (red, green, blue) in a layer sequence. Because of the small layer thickness (about 300 nm altogether), realizations are possible on flexible undersurfaces (plastic foil and/or metal foil). One problem is the high sensitivity to oxygen and water. In order to stabilize the OLED, the substrate is glued with a further glass cap and/or coated by means of a thin-layer sequence of inorganic and/or organic layers.